“Straub” type couplings are formed of a unitary band having free ends which are subjected to tangential tension force to clamp the band around pipe elements to be joined end to end. Under the tension force, the band deforms radially inwardly to encompass a smaller diameter and forces toothed retainer rings captured between the band and the pipe elements into engagement with the pipe elements. Deformation of the band also compresses a seal against the pipe elements to ensure a fluid-tight joint. Examples of Straub type couplings are disclosed in U.S. Pat. Nos. 4,629,217, 4,664,422, 5,137,305 and 5,280,970.
Joints formed by Straub type couplings are often flexible in bending. While bending flexibility is sometimes desired in piping networks, for those situations when more rigidity in bending is needed, Straub type couplings are inappropriate. There is clearly a need for a coupling which combines the advantages of the Straub type coupling with the increased bending stiffness normally associated with other types of mechanical couplings.